Observations of the volume flux of a seafloor hydrothermal plume using an acoustic imaging sonar

Abstract

We present a 26 day time series (October 2010) of physical properties (volume flux, flow velocity, expansion rate) of a vigorous deep-sea hydrothermal plume measured using our Cabled Observatory Vent Imaging Sonar (COVIS), which is connected to the Northeast Pacific Time Series Underwater Experiment Canada Cabled Observatory at the Main Endeavour Field on the Juan de Fuca Ridge. COVIS quantitatively monitors the initial buoyant rise of the plume from ∼5 m to ∼15 m above the vents. The time series exhibits temporal variations of the plume vertical volume flux (1.93-5.09 m3/s), centerline vertical velocity component (0.11-0.24 m/s) and expansion rate (0.082-0.21 m/m); these variations have major spectral peaks at semidiurnal (∼2 cycle/day) and inertial oscillation (∼1.5 cycle/day) frequencies. The plume expansion rate (average ∼0.14 m/m) is inversely proportional to the plume centerline vertical velocity component (coefficient of determination R2∼0.5). This inverse proportionality, as well as the semidiurnal frequency, indicates interaction between the plume and ambient ocean currents consistent with an entrainment of ambient seawater that increases with the magnitude of ambient currents. The inertial oscillations observed in the time series provide evidence for the influence of surface storms on the dynamics of hydrothermal plumes. Key Points COVIS is capable of long-term, quantitative monitoring of a hydrothermal plume Plume flow velocity and volume flux show significant temporal variations Tidal flows affect the plume flow velocity via the current-driven entrainment ©2013. American Geophysical Union. All Rights Reserved.